This invention relates generally to methods and apparatus for resampling of data and more particularly to methods and apparatus for resampling three dimensional datasets for visual processing and display of medical data.
In at least one known computed tomography (CT) imaging system configuration, an x-ray source projects a fan-shaped beam which is collimated to lie within an X-Y plane of a Cartesian coordinate system and generally referred to as the xe2x80x9cimaging planexe2x80x9d. The x-ray beam passes through the object being imaged, such as a patient. The beam, after being attenuated by the object, impinges upon an array of radiation detectors. The intensity of the attenuated beam radiation received at the detector array is dependent upon the attenuation of the x-ray beam by the object. Each detector element of the array produces a separate electrical signal that is a measurement of the beam attenuation at the detector location. The attenuation measurements from all the detectors are acquired separately to produce a transmission profile.
In known third generation CT systems, the x-ray source and the detector array are rotated with a gantry within the imaging plane and around the object to be imaged so that the angle at which the x-ray beam intersects the object constantly changes. A group of x-ray attenuation measurements, i.e., projection data, from the detector array at one gantry angle is referred to as a xe2x80x9cviewxe2x80x9d. A xe2x80x9cscanxe2x80x9d of the object comprises a set of views made at different gantry angles, or view angles, during one revolution of the x-ray source and detector. In an axial scan, the projection data is processed to construct an image that corresponds to a two dimensional slice taken through the object. One method for reconstructing an image from a set of projection data is referred to in the art as the filtered back projection technique. This process converts the attenuation measurements from a scan into integers called xe2x80x9cCT numbersxe2x80x9d or xe2x80x9cHounsfield unitsxe2x80x9d, which are used to control the brightness of a corresponding pixel on a cathode ray tube display. These integers form a volume of medical data.
One popular visualization technique for medical applications is to resample a volume of medical data acquired from a CT or MRI imaging system along a plane of arbitrary slope. This visualization technique is known as a reformat. Volume resampling along a plane is commonly called a reformat of a given volume. Reformatting allows viewing of cross-sections of pathology and provides the ability to take accurate measurements of strictures, aneurysms, areas, and distances, among other things.
Determining the placement of a resampling plane could be facilitated by interactive placement. Interactive placement would provide for the display of a first reformat plane image followed by the production and display of a new reformat plane image, where the new reformat plane is incrementally different in scale, rotation, or translation from the first reformat plane. Interactive placement, however, demands good resampling performance of the data, usually requiring about 10 reformat images per second to be generated. Without adequate performance, interactive placement is difficult to control. Systems known to date have not been capable of providing adequate resampling performance.
Accordingly, it would be desirable to rapidly and efficiently resample a three-dimensional volume of data to permit efficient interactive viewing and visualization of medical data. It would also be desirable to provide efficient clipping of resampling surfaces. In addition, it would be desirable to provide efficient management of optimized resampling functions, where large sets of highly optimized and specialized functions are used for resampling.
In one embodiment, these and other advantages are attained by a method for rapidly resampling a three-dimensional volume of data to permit efficient interactive viewing and visualization of the data in which a set of parallel line segments defining a surface having a constant slope in at least one direction and intersecting the three-dimensional volume are selected and the data is processed at points on the parallel line segments to generate a reformatted image of the data. A corresponding apparatus embodiment is provided. Using the methods and apparatus embodiments of this invention allows processing of data to proceed quickly because it is not necessary to check the parallel line segments during processing of the points on the segments to determine whether the points are within a given data volume. Furthermore, the methods and apparatus embodiments allow rapid and efficient resampling of a three-dimensional volume of data, for example, medical data, to be achieved through use of sets of highly optimized and specialized resampling functions.